This is a transformer used in professional sound distribution systems where signals need to travel a long way, shops, pubs offices etc.
There are 4 taps depending on the wattage required at 8 Ohms..
This transformer it seeems has a tap at 50 volts
It has a metal clamp and size of the main body is 55mm x 45mm high 57mm wide to edge of pins
Hole spacing 70mm.